Solution-processed polymer semiconductors are key materials in the fabrication of lightweight, low-cost, and flexible electronic devices without using the high-vacuum process. For practical applications, reliable device operations based on these materials are required. In this study, we propose a strategy to improve the operation stability of organic field-effect transistors (OFETs) using solution-processed polymer semiconductor/insulator blends as the active channel prepared by introducing a fluorinated insulating polymer in the blends. The semiconducting polymer forms nanowire networks in spin-coated ternary blend films, which serve as charge transport pathways in the insulating polymer matrix consisting of the fluorinated polymer and polystyrene. Owing to its high surface potential attributed to the strongly electron-withdrawing structure, the fluorinated polymer provides a large energy barrier for suppression of the hole trapping at the semiconductor/insulator interface. Consequently, OFETs based on the ternary blend films with an optimized polymer composition exhibit almost hysteresis-free transfer and output characteristics and superior electrical stabilities under sustained gate-bias stresses in both N-2 and air atmospheres. We believe that our study provides a practical route to the fabrication of OFETs based on polymer semiconductor/insulator blend systems with high operation stabilities.